I thing part of the mythology about the 10x engineer stems from the very real and shockingly widespread existence of the NNPP or the "Net Negative Producing Programmer".

There are many environments in which NNPP's are pretty much the standard, programmers that produce more problems and bugs than actual working and sustainable solutions.

In such an environment any competent developer will quickly stand out and will easily be labelled as a "x-times engineer", when all they actually are is just good at their job where others fail miserably.

The 10x myth is a way to give a positive spin on the shockingly common incompetence in our field.